Thermodynamics of nitrogen in Mn-Fe-C melts
- PDF / 201,815 Bytes
- 7 Pages / 606.24 x 786 pts Page_size
- 28 Downloads / 211 Views
10/31/03
10:25 AM
Page 853
Thermodynamics of Nitrogen in Mn-Fe-C Melts YOUNG E. LEE The present study assesses the available experimental data in the Unified Interaction Parameter (UIP) formalism and proposes a thermodynamic model to describe the solubility of nitrogen over the entire composition range in Mn-Fe-C melts. The solubility of nitrogen was investigated from equilibrium between gaseous nitrogen and nitrogen dissolved in Mn-Fe-C melts. 1/2 N2 (g) N (x, liq. Mn)
K xN gN /PN21/2
The equilibrium constant, K, and the activity coefficient of nitrogen, N, in the UIP formalism were determined taking a liquid Mn and infinite dilution of N in a Mn melt as the standard states for Mn and N, respectively. ln K 5.633 5770/T
(1544 to 1841 K)
ln gN 1/2 CC xC 2/3 CCC xC 3 1/2 FeFe xFe 2 2/3 FeFeFe xFe 3 CFe xC xFe 2 CCFe xC 2 xFe 2 CFeFe xC xFe 2 NN (xN 1/2 xN 2) NNN (xN 2 2/3 xN 3) CN (xC xC xN) CCN (xC 2 2 xC 2 xN) CNN (2 xC xN 2 xC xN 2) FeN (xFe xFe xN) FeFeN (x Fe 2 2 xFe 2 xN) FeNN (2 xFe xN 2 xFe xN 2) CFeN (2 xC xFe 4 xC xFe xN) 2
˛
˛
˛
˛
˛
˛˛˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
˛
where CC 9.24 16,060/T, CCC 51.8 157,800/T, FeFe 0, FeFeFe 0, CFe 7.52 7250/T, CCFe 8.39 16,190/T, CFeFe 9.93 12,790/T, NN 16.2 19,020/T, NNN 0, CN 27.61 45,200/T, CCN 53.41 172,000/T, CNN 0, FeN 15.53 21,300/T, FeFeN 15.48 28,300/T, FeNN 0, and CFeN 32.9 63,800/T.
I. INTRODUCTION
NITROGEN in steel is regarded as a detrimental impurity element when the issues of strain aging and embrittlement are of primary concern; in these cases, its content is limited to the lowest practical level. At the same time, it is considered a beneficial alloying element when mechanical strength and corrosion resistance are important criteria. In these applications, it is maintained at the desired concentration in steels. A suitable nitrogen content is attained by a careful choice of steelmaking practices. Effective control of nitrogen requires a good understanding of the behavior of nitrogen under steelmaking conditions. The solubility of nitrogen in steel melts is one such fundamental information. Many investigators in the past had studied the solubility of nitrogen in iron alloy melts, and most have accepted the experimental results by Pehlke and Elliott.[1] Recently, the Japan Society for the Promotion of Science[2] assessed the preceding nitrogen solubility information, including the latest results. They recommended new values. Both sets of values are similar to each other, but their dependency on temperature is slightly different. The aforementioned information was developed with iron as a solvent, and the contents of alloying elements limited to the terminal region of iron. When the contents of alloying elements exceed their effective range, the recommended values may not adequately describe the behavior of nitrogen. YOUNG E. LEE, Senior Specialist, is with Eramet Marietta, Inc., Mariet
Data Loading...
